7 Answers
7

I would strongly suggest using indoor lights so you have complete control. Have the complete setup (with strobes and backdrop) done before they meet you. Do a trial run with your friends/model and tweak all the parameters till you get that perfect shot, so all the professionals have to do, when they meet you, is sit on a chair, look a certain direction and you just click the camera without thinking about anything(using the settings you had already set earlier).

This is a simple setup using a cheap 83cm umbrella and 40cm softbox with two $80 Yongnuo YN-560 manual speedlites triggered with RF-602 wireless triggers. I'd probably put this basic lighting gear at about $350-400 and it's served me very well.

This is by no means the only lighting setup you could use for a business portrait, but it produces decent results.

Getting some cheap lighting gear like this will really open up a lot of opportunities to sculpt your lighting the way you want.

The great thing about using strobes like this is that you're running pretty close to ISO 100 which will yield very sharp results.

You can of course use natural light and use it effectively but I guess it's up to the needs of the design as to what sort of look you need to capture.

The biggest thing that comes to mind based on what you've described is that you'll need supplemental lighting. If all you're working with is overhead light, you're going to have a lot of shadows in the eye sockets, under the nose, under the chin, etc. It'll work great for a monster movie, but not so much for a business portrait.

This lighting might come in the form of continuous lighting, strobes, or even by having an assistant or a light stand that's holding a reflector to reflect some of the overhead light back into the shadows.

The following goal is assumed:
You are not for artwork but for reliable, repeating results on which the employees are easily recognised and don't look too bad.

Any modern SLR does this and practically any lens does.
Even any compact camera would do.

I'd go for a canon 1200D or similar and a 50mm 1.8 lens (or the 40mm pancake).

Go for a fixed focus lens, whatever brand you take. This makes the procedure easy. One thing less, that anybody could do wrong.
Well, there is nothing wrong with other focal lengths, unless they are way too short or long. But zoom lenses can be zoomed and the focal length has significant impact perspective (don't take this literally) and the way the proportions of a face or head are displayed in the image.

Use a Tripod.

Make sure, that the distance from the center of the tripod (and the camera) is always the same to the chair for the "model" and the background.

Do have some distance to the background.

Use two studio flashlights of any well known brand. Doing so you have good chances for getting them repaired or even replaced equally without adjusting your procedure.

Use two equal soft boxes or reflex umbrellas. Don't go for shine-through umbrellas.
Beauty-Dishes could be even better for your purpose. They are more expensive though.
If you use shine-through umbrellas then don't forget to consider the length of the pin (sorry for my bad English), I mean where exactly it is mounted. Or even mark the pin so that anybody can easily re-build exactly the same set.
If it is within the budget, then go for beauty dishes.

If you choose a dark background, which I don't recommend for this purpose, then budget in a third flashlight with a snoot or barn doors as head light. This comes from behind and high and is of importance for dark hair or dark clothes. It helps separating the dark motif from the background.

Your procedure should include a good example on how the final image should look like. And add good making-offs. Produce them with a friend/colleague. Take time, adjust everything and finally document the set.
Measure everything. The distance between flash and model is of vast importance. Document exactly between which details the distance should be measured. The middle of the lights' tripods/stands and the middle of the chair is quite practical for any later re-production of the same set.
Don't forget the height of the light and their angle.

Top-Down-Angle you can describe in degrees. That is easy to reproduce anyway because it is a no-brainer that the light must "hit" the model's face.
The horizontal angle is best described with the time on the watch. Imagine - and draw it that way in your documentation - the model is in the middle of the clock-face an position the camera on 6 o'clock. For all flashlights find their corresponding time of the day.

Try various poses for the direction of the body, the direction the face should look to (the eyes will look into the camera but the face may just pass it) and the angle the head is held and discuss the results with the managers in charge.

Try different light settings. 1/1 and 1/1 is practically the same as 1/64 and 1/64, but 1/4 and 1/8 makes much of a difference. I'd go for one step distance but give it a try and decide yourself.

For the sake of a repeatable process, power one of the flashes at 1/1. (250Ws should do. 150 should be enough in most settings of this type. I'd go for 300Ws. More than that is not reasonable.)
Using this flash at full power - one of them - reduces the importance of the surrounding lights. And that erases an error source and therefore makes the process easily repeatable.

For an easy to use process, set the camera to a fix white balancing value for flash lights. That is something to consider when you decide for the model, although I guess that every modern SLR should have that setting.

Color Checkers etc. are way over-done for this purpose but they add additional chances for making mistakes. Wrong use of these methods will result in far worse results than not using them at all. Your light is constant. For repeatable results a constant white balance is all you need.

Document it in a way, that the final image is smaller than the image taken. By doing so you can ensure that the portraits really are equal in the finishing process, which ideally is reduced to a proper, always similar, cut of the image taken. So let the photographer take a bit more on any side for having the space to crop.
Humans, unlike products, are of different size. :-)

Add some cosmetic powder in various shades (for various colours of skin that are around) and add to the photographers checklist, that (larger) glares should be powders. For men and women alike!

The program is M. No automatics. No auto-ISO, no AWB, everything fix.
Document the aperture, the ISO setting, and the exposure time, although that is less important. Use something save but fast enough to minimize the influence of the surrounding available light. 1/200s or 1/160s is my guess.
If you ignore my advice and buy a zoom lens, then do document the focal length to be used!

That's basically it for the photo booth itself and for the photographer's process.

Your company should define some dress code suitable to your company's business and/or the various roles. And consider this dress code when you select the background colour.

Talking about the background. Don't be too colourful, unless you are writing from India or Bangladesh. I mean your cultural environment has naturally an impact on that decision. But colours are difficult especially when the ladies are allowed to wear any fashionable colour they want. I would choose a gray to white gradient.
(Well, I myself would use dark gray and set a spot light just behind the head. But that is probably too advanced for a process that must be easy to repeat)

And before you guys really photograph every single employee, test the process with two or thee of them, use somebody else to build the set based on your docs only and - important - get the image printed on the badge. When you see the final result on the badge, there is a good chance that you want to amend the settings, background etc.

In addition to what others have said, my only note is that bright direct sunlight will create very sharp contrasts and is likely to create some overexposed areas. Either avoid direct sunlight in the composition, or carry a big sheet of cheesecloth or other similar material that can be used as a screen to diffuse the light.

On the last photkina I listened to a pro photographer who told about the role of smartphone cameras in a professional environment.

He had a job the other day for a local non commercial soccer club with limited budget to photograph each individual player for their website and other usages.

In order to keep the cost low he found a way of getting rid of the post processing. For doing so he took one of the players in their team dress and chose an available light set with some plain white background and some nice light soft daylight though a window.
Then the tried a number of these tons of instagram type apps and chose an app/filter combination that suited well to the team dress and that the customer liked.

Once that was done the acutal job was quick and easy. Every player was shot at this very spot, pictures downloaded, done.